The chemical senses serve a major function in influencing food selection and intake and therefore nutritional status. The purpose of this research program is to delineate the psychophysical characteristics of an understudied chemosensory system, that which mediates oral chemical irritation, or the "common chemical sense." Proposed experiments include examination of 1) differences among stimuli regarding the rate of growth of sensation intensity with concentration and the rate of sensation decay over time, 2) potential qualitative discrimination in this sensory system, 3) interactions of oral irritation with the classical gustatory qualities, 4) differences in sensitivity across the oral epithelium, 5) spatial summation, 6) the time course of sensory adaptation and possible desensitizing effects of some oral irritants, and 7) the relative contributions of facial nerve (chorda tympani) and trigemimal nerve afferents to the perception of irritation on the dorsal tongue surface. This latter comparison will be achieved using patients with unilateral chorda tympani transection, stimulating each half of the tongue separately. A final underlying theme will examine differences in perception among individuals with chronic high dietary levels of spice-derived irritants, which are reported to alter oral sensitivity. The proposed experiments should provide information basic to the understanding of any sensory system: psychophysical functions, the nature of adaptation and inhibition, and differences in sensation due to different spatial and temporal parameters of stimulation. These studies should pave the way for future correlation of perceptual characteristics with physiological observations (e.g. relation of sensation to receptor types) or with chemical characteristics of oral irritants (e.g. structure-activity studies). These data should also provide a picture of "normal" common chemical sense function, against which future studies of disordered oral sensation may compare results.